Mine roof bolt



May 7, 1968 A. ASKEY MINE ROQF BOLT Filed May 9, 1966 FIG. 2

AQTHLLK fiskey QE MJW United States Patent 3,381,567 MINE ROOF BOLT Arthur Askey, Heidelberg, Transvaal, Republic of South Africa, assignor to Torque Tension Bolt Company (Proprietary) Limited, Heidelberg, Transvaal, Republic of South Africa Filed May 9, 1966, Ser. No. 548,682 5 Claims. (Cl. 85-75) ABSTRACT OF THE DISCLOSURE An expan-sible mining roof bolt is disclosed having a coned nut and a pair of separate arcuately shaped leaves separable into four segments associated with the outer surface of the coned nut. The inner surfaces of the leaves are tapered at an angle less than the cone angle of the surface of the nut. Symmetrical corrugations'or serrations are formed on the outer surface of the leaves for gripping action.

This invention relates to roof bolts used to anchor bolts or studs of varying length into holes drilled into rock strata. These bolts are well known as root bolts in the mining industry.

There are a number of known roof bolts, many of them specifically constructed for use in particular types of ground and to suit special conditions. The bolt of applic'ants invention is used to serve a variety of purposes in mining operations such as clamping of rock strata to secure the hanging, or for forming a base .for the suspension or anchoring of equipment used in mining operations. It is essential that such bolts should remain securely fixed in the rock and not be liable to axial or rotational movement in the hole in the rock.

it is the object of this invention to provide a bolt having a small number of parts shaped to give the maximum holding area even when used in soft or friable ground, and at the same time to reduce, as far as possible, any tendency for any of the few parts used to be rotated in the hole in the ground.

According to this invention there is provided a roof bolt comprising a circular cone-shaped nut adapted to be engaged on a screw-threaded rod, said nut having a cone angle of between 5 and a pair of diametrically oppositely disposed longitudinal fins on the outer surface of the cone, a pair of arcuately shaped leaves associated with the outer surface of the cone and having inner surfaces tapered at an angle of about 2 less than the cone angle, longitudinal slots down said leaves to receive the fins, said slots extending from the wide portion of the leaves down towards and close to the narrow end, serrations formed on the outer surface of the leaves, said serrations being symmetrical about their greatest diameters, and a plate held on said rod to support the narrow ends of the leaves.

Further features of. this invention provide for a resilient disposable strap to be provided around the leaves to temporarily hold the leaves onto the cone-shaped nut.

Still further features of this invention will become apparent from the following description of the preferred form of this invention. In this form the roof bolt is made of materials having not only strength under tension but also a toughness to resist any erosion which might take place. Malleable metal castings for the leaves meet these conditions.

This embodiment will be described with reference to the accompanying drawings in which:

'FIG. 1 is an exploded view showing all the parts with the leaves partly in sect-ion, and

FIG. 2 is a completely assembled roof bolt with the components shown at right angles to that shown in FIG. 1.

Referring to the drawings, the bolt or stud I l constituting a screwthreaded rod, is screw-threaded at 12 a suitable distance down from the top end 13. On the screwed end 12 is a cone shaped nut 14 adapted to be inserted into a shell which is formed by a pair of leaves 15. The cone angle of the nut is made to be 7 and the inner surfaces of the leaves are also tapered in a manner complementary to the nut but the angle of the taper is made about 2 less than that of the nut.

The leaves 15 are made of any convenient length and are provided on the outside with serrations or corrugations 16 adapted to bite into the walls of the hole in which the roof bolt is inserted. The insides of the leaves are likewise corrugated. The serrations are a particular feature of this invention in that they are not of the usual saw tooth shape but are symmetrical about their greatest diameters. It is found that a buttress effect is obtained by the use of these serrations when the leaves are made to penetrate strata of soft or friable rock. There is less tendency for this shape of serration to tear the rock when an axial loading is applied to the IOOlf bolt in the operatively positioned unit. The angle between adjacent sides of the serrations is preferably about to It is to be remembered that the leaves '15 must be sufiiciently long to provide adequate grip in the rock and also to ensure that maximum expansion will take place between the leaves before the coned nut 14 can project below the lower edges of the leaves 15. With the angles for the cone and leaves as given above, the preferred length of the leaves will be 70 mm. Also the serrations are made as deep as practically possible consistent with the thickness of the leaf wall.

Each leaf 1:5 is divided longitudinally preferably into two equal segments 17 and the coned nut 14 has two oppositely disposed projecting fins 1 8 which will keep it from turning by enter-ing the slot 19 bet-ween the segments 17 of the leaf 15. The slot 1 9 dividing the leaf into two segments extends downwardly from the top or wide end of the leaf towards the bottom or narrow end. The slot 19 does' not however reach this n'arrow end and consequently the segments are held together by a narrow strip 25 and the bottom end 21 Olf the tapered cone 14 is chamfered so that its bottom edge tends to wedge in between the segments 17.

Frequently the leaves, or similar parts which are used in a roof bolt, are tied together with a bail which is often somewhat cumbersome in use. However, in the roof bolt according to this invention the bolt 1 1 is provided with a washer 22 or similar stop', rigidly secured to the bolt below the leaves 15 to act as a support for the segments 17 which are held together with a disposable band 23, such, for example, as that shown as a thin band of plastics material.

Care is taken, in assembling the parts for insertion into the hole, to see that the fins 18 are engaged in the slots 19. The use of the sleeve 23 will hold the parts in proper position during the initial insertion of the roof bolt into the hole. Should the fin 18 jump out of its slot 19 during the initial insertion of the roof bolt the rounded ends 24 of the segments will tend to discourage its engagement between the segments 17 and allow it to slip a short distance to be engaged more firmly in a slot 19, the sleeve 28 assisting it springing and holding the parts in this desired position.

In the arrangement described the fins 18 on the cone 14 enter the slots 19. In some prior constructions having finned coned nuts, the fins enter the spaces between the leaves 15. The arrangement described holds the cone 14,

that is in its function as a nut, from turning and allows the screw 12 to draw the'cone 14 along the thread '12 to more efficiently spread the shell formed by the segmented leaves 15.

It will be appreciated that the assembly above described will be made to various sizes to meet particular requirements whilst maintaining the basic design features.

The roof bolt is used in the usual manner for such articles. Before insertion in the drilled hole, the cone nut 14 can be screwed to any suitable position within the leaves in order to suit variations in hole diameter met with in practice. The shell is made to enter the hole as a snug fit so as to initiate expansion. When inserted in place the stud 1 1 is turned to draw the cone 14 into the shell which is thereby spread so that its serrations 16 engage the wall of the hole. If the hole in the rock has a diameter only slightly larger than the outside diameter of the shell, a slight pull on stud 11 in a direction away from the roof bolt, or a slight turning of the stud or bolt 11, will draw the nut 14 into the shell to spread its segments 17 and press them into the rock wall.

Where soft or friable rock strata are encountered the leaves will be further expanded, and a fracture of the strips of metal 25 will take place. This will enable the parts to deform in a substantially parallel manner as the cone descends between them, thus avoiding burring or very high friction between the'parts. It is an important feature of this invention that the angles of cone nut and leaves, and the size of the strip 25, enable maximum lateral pressure to be exerted on the leaves to anchor the roof bolt in the hole while also maintaining the friction between the descending cone and .the outwardly expanding segments as low as possible.

The plate or the like (not shown) which is to be clamped by the bolt 11 is conveniently bolted onto the end of the bolt 11 projecting from the rock face. The end of the bolt 11 may be screwed and fitted with a nut for this purpose.

The screw thread on such projecting end conveniently allows the nut to be tightened on a plate or the like from time to time. It is however obvious that the more tension there is applied to the roof bolt when in place the greater the grip it will make in the wall of the hole in the ground.

It will be appreciated that other materials than those described may be used without departing from the scope of this invention.

What I claim as new and desire to secure by Letters Patent is:

'1. A roof bolt comprising an internally screw threaded nut, a cone shaped outer surface on said nut, said outer surface having a cone angle of between 5 and 10, a pair of diametrically oppositely disposed longitudinal fins on said outer surface, a pair of separate leaves each arcuate in cross section, positioned on the outer surface of the nut and the inner cone contacting surfaces to said leaves being tapered at an angle of about 2 less than the cone angle of the outer surface of the nut, longitudinal slots in said leaves receiving the fins, said' slots extending from the wider ends of the leaves towards and close to the opposite ends thereof and corrugations formed on the "outer surface of the leaves, said corrugations being symmetrical about their greatest diameters, and a supporting plate mounted on the bolt for the leaves.

'2. A roof bolt as defined in claim 1 wherein the cone angle is 7, the angle of the tapered inner surfaces of the leaves is 5 and the material of the leaves is malleable cast iron.

3. A roof bolt as defined in claim 1 wherein the length of the leaves is mm. and the angle between the sides of adjacent corrugations is about to '4. A roof bolt as defined in claim 1 wherein the edges of the tapered inner surfaces of the leaves adjacent the wider ends of the latter are ch'amfered and the correspond-ing edges of the leaves adjacent said tapered inner surfaces are rounded, the small end of the cone-shaped nut also being chamfered.

5. A roof bolt as defined in claim 1, wherein the inner surface of said leaves is likewise corrugated.

References Cited UNITED STATES PATENTS 1,434,394 =1l/ 1922 Matthes 85-75 1,469,667 10/1923 Pleister 85-72 2,120,279 6/ 1938 Heirs 85-72 2,252,316 8/1941 Gelpcke 85-74 2,625,071 =1/1953 Lewis 85-75 2,878,709 3/1959 H'orvath 85-87 3,110,212 11/1963 Wing et al. 85-74 FOREIGN PATENTS 692,742 8/ 1964 Canada.

374,701 9/1930 France. 1,143,772 2/1963 Germany.

MARION PARSONS, JR., Primary Examiner. 

